Jinbei handling marine battleships on his own wasn't that much? That chapter named after him pretty much showed how awesome his abilities in water are.
Jinbei handling fodders with a single punch? Check.
Jinbei owning Moria's zombies AND one-shoting Moria himself? Check.We're just talking about what we have seen of Hancock, which is not much. In theory, she could be a beast in combat. Imagine her having all of her sisters's skills plus her own Haoshoku Haki and Devil Fruit. It could go as this: she uses Snake-Hair Possession to become Medusa-like and ON FIRE, deflecting blows back to the attackers and predicting everyone's movements. THEN she goes around the battlefield, kicking and snake-hair-biting everyone and turning them to stone. And all fodders trying to escape suddenly faint from her Haki.
Now THAT would be overpowered!
Jinbei handling marine battleships on his own wasn't that much? That chapter named after him pretty much showed how awesome his abilities in water are.
Boa and co are able to travel and eat sea kings. And she had a named chapter about her as well
Jinbei handling fodders with a single punch? Check. Boa handling fodders wthout to attack
Jinbei owning Moria's zombies AND one-shoting Moria himself? Check. Smoker and Pxs
I'm not saying both are too strong to join, just that Boa isn't paling infront of the other Shichibukai and I see more than enough.
But to put it simply… I'm aware of one think. The Robin/Frank syndrom.
Both were introduced as super powerful and Robin as haxed. And right now they are below the monster trio. I could see, even if hardly, be Jinbei in the monster trio theme as well but I never could see him under Sanji or Zoro. That would be strange. I would be ok if he is above Sanji but that on other hand would destroy the whole Sanji/Zoro argument if suddenly Jinbei is between them and the rivaly of them would be without sense.
No it isn't the Sanji fanboy in me saying this. But the whole discussions and the whole rivaly theme done by Oda himself would be pointless.
And for Boa I feel even worse. She could be a second Robin. Pretty hax abilities but she will pale, "down-graded" below the monster trio. I can't see her doing that bad-ass stuff and looking cool like the monster trio (even she could own Sanji anytime soon with her charme 
).
I was that sure that Oda would put Franky to that level and introduce him to monster trio level but ever since EL he is paling infront of them. (see TB and against PX who was the leading fighting force)
it seems that Oda want to keep this 3 monsters theme.
That's why I hoped some other girl like Marguarite would join the crew. She hadn't to be downgraded or whatever and we have a nice female addition to the crew. Don't get me wrong maybe Oda will put Boa, if she joins, in that usual monter trio theme, but I somehow can't see that. And downgrading Jinbei below Sanji level to keep the rivaly theme and all the argumenting in all forums would be a slap into the face of Jinbei.
EDIT
Just for the lulz... Could you see Jinbei or Boa being that bad-ass in a spread like this...
